(1) Field of the Invention
The invention relates to the use of hyperspectral sensing and classification techniques, originally developed for defence applications, for the automated identification and sorting of household waste. Reclaimed material may then be recycled. The application is for general household waste and does not cover types of waste with specific hazards, e.g. nuclear waste. However, the invention could be adapted to other waste streams or sorting applications.
(2) Description of the Art
Household waste is currently sorted in Material Reclamation Facilities (MRFs). These generally use mechanical devices to achieve sorting of waste types based on material or object properties such as size. For example, a trommel (a rotating drum with holes) can be used to separate containers from paper and film waste. These devices are generally rather crude and cannot sort different grades of the same material, eg different types of plastic or coloured glass. Manual sorting is widely used in MRFs to achieve separation of plastics, glass, and paper or to achieve quality control by removal of contaminating items from separated streams of such materials. In recent years, some higher technology equipment has been developed but such instances tend to be focussed at sorting one specific material at a time. For example, high-density polyethylene (HDPE) from a mixed plastics stream, followed by polypropylene (PP) extraction from the same stream and so on.
There are now a number of systems that carry out automated identification and sorting systems for material reclamation processes. Most employ some form of near-infrared identification process for material classification and an air ejection process to sort the identified objects. These types of systems are primarily focused at specific material types and have generally only successfully been applied to plastics sorting where they are used to sort different types of plastic from one another. These systems are, therefore, dependent on some form of upstream processing to sort plastics from mixed household waste before the technology can be applied.
In addition to sorting plastics into their main types, some of these systems will also sort plastics by colour and may even remove cartons if present within the waste stream.
U.S. Pat. No. 5,260,576 refers to a technique for measuring the transmittance of objects using X-ray radiation, however the technique has only been successfully applied to plastic containers, rather than a wide range of materials.
Published European patent application number EP 1 026 486 discloses a relay lens system allowing an object to be illuminated by a source, and the reflected radiation collected in one of two ways, according to whether the reflection from the object is diffuse or specular in nature. This system is intended for sorting plastic materials only for recycling, rather than sorting objects of a variety of different materials, such as is found in general domestic waste.
Published European patent application EP 0 554 850 describes a method of classifying plastic objects based on measuring the infra-red transmission of the objects. The method is not applicable to other classes of waste.
Existing sensing technologies can only identify and classify a limited range of materials. Some systems exist for classifying materials within a class, e.g. different plastics, but these systems have been optimised for that task and would be unable, for example, to identify an aluminium can mixed in with other waste.
Certain systems exist which use a small number of wavelength bands to image and then classify materials, for example that described in US patent application 2002/0135760 images in only three or four wavelength bands, which is sufficient to achieve the purpose of that system, namely simple distinguishing of contaminated (dirty) chicken carcasses and uncontaminated (clean) carcasses. However such a multispectral system would be unable to distinguish a large number of different material types.